The energy provided by sun and wind is intermittent and often needs a back-up system;
The gravity-based energy storage system
One of these is the Energy Vault. When a solar farm produces extra electricity during the day, giant robotic cranes use that energy to lift and stack thousands of 38.5 ton (35 tonne) blocks into a tower as high as 500 ft. (152 m) the bricks storing energy through the elevation gain.
When the sun isn’t shining or the wind is not blowing, software tells the system to lower the bricks, the weight of which will drive generators as the crane plucks them off the tower and lowers them to the ground, so sending electricity back into the grid. The system can respond within a millisecond.
The development of this technology took place at Idealab, the Pasadena, California-based startup incubator, then was handed to Energy Vault, to commercialize the technology.
In partnership with Italian energy company ENEL, a tenth the size of a full-scale operation was built and trialled in Biasca, Switzerland, north of Milan, Italy. A Swiss subsidiary of Mexico-based CEMEX Ventures provided venture capital, concrete and other composite material technology.
The unit, from proposition to working prototype, took about nine months and less than US$2 million to accomplish. The Energy Vault team was led by Andrea Pedretti, inventor with more than 25 patents worldwide for a variety of civil engineering and energy applications.
Having earned his M.Sc. in structural engineering from the Swiss Federal Institute of Technology in Zürich, Pedretti worked with Airlight Energy, a Swiss cleantech provider focusing on unique solutions for concentrated solar power.
The Energy Vault system could deliver as much as 80 MW-hours of power, enough to cover about 60,000 homes for up to 16 hours The system is modular and flexible with each plant having a capacity of between 10 and 35MWh and a power output of between 2 and 5MW.
Each tower can be erected quickly; the cranes can be delivered within months and erected within weeks, without the huge investment of a battery factory.
The bricks themselves can be made on-site from materials such as soil concrete construction debris which would otherwise go to a landfill. At a coal plant that plans to close and reopen renewable energy on-site, the bricks could be made from coal ash.
India’s Tata Power is the company’s first announced customer, with a tower that will be constructed in 2021. But Energy Vault is in talks with other customers about more than 1,200 potential towers.
In August 2019, Energy Vault raised US$110 million from SoftBank Vision Fund to take its next steps in the world. One place where the Energy Vault technology could be used to advantage is around desalination plants in places such as sub-Saharan Africa or desert areas.
In Scotland , Peter Fraenkel at Gravitricity is working with the Edinburgh University Institute for Energy Systems and Dutch winch and offshore manufacturer Huisman Equipment BV on a solution in the 1MW to 20 MW power range which suspends weights of 500 – 5000 tonnes in a deep shaft by a number of cables, each of which is engaged with a winch capable of lifting its share of the weight.
The pilot plant, involving a 16m high rig is being assembled at a grid-connected site at the port of Leith for testing to begin in spring 2021.
What you can do: Tell electricity supply companies and town planners about gravity-based energy storage systems
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